Something Awful solved this problem twenty years ago by charging a small fee ($5) to register an account. "Banned" users could re-activate their account by paying the fee again. "Permabanned" users would have to jump through more steps like different email addresses and payment methods. This upped the investment required for casual toxic trolling.

But this was for an old school "centralized" forum. Not sure what "paying for an account" would entail for a decentralized network.